Abstract There is an urgent need to develop prevention options to halt the progression of oral premalignant lesions (OPL) into oral squamous cell carcinoma (OSCC), a disease that results in over 250,000 deaths each year worldwide. Our recent findings indicate that the activation of the PI3K/mTOR signaling network is the most frequently dysregulated molecular mechanism in OSCC and OPL and that PI3K/mTOR inhibition exerts potent antitumor activity in experimental OPL and OSCC models. We also showed that the repurposed drug metformin, which is safely used by millions of type 2 diabetes patients, decreases mTOR signaling in OPL and OSCC and displays potent chemopreventive activity in experimental oral premalignancy models. Based on these studies, and recent epidemiological data showing a significant reduction in OSCC incidence in diabetic patients on metformin, we have recently launched the NCI N01 Phase IIa Clinical Trial of metformin for oral cancer prevention trial (M4OC- Prevent, NCT02581137) to explore the potential use of metformin for OSCC prevention. However, our incomplete understanding of the molecular determinants of the therapeutic response to metformin in OPL or in any other precancer lesions limits our ability to identify patients most likely to benefit from metformin. The overall objective of our project is to elucidate the molecular mechanisms by which metformin acts on OPL and OSCC to 1) discover novel genomic markers of response and resistance to metformin in OPL, 2) test the influence of bioenergetic pathways involving LKB1/AMPK, and mTOR and YAP inhibition in the activity of metformin in OPL, and 3) apply genetic screens to identify novel molecular mechanism determining response or resistance to metformin, thereby helping prevent or overcome drug resistance. By leveraging the wealth of clinical and genetic information and tissue and body fluid resources from our M4OC-Prevent trial with our expertise in decoding cancer promoting pathways, the long-term goal of our team effort is to define mechanism-based biomarkers predicting a response to metformin and suitable therapeutic options to overcome drug resistance. Ultimately, our planned studies will provide the foundation for patient selection (enrichment) for the design and implementation of future OSCC precision prevention trials. By focusing on a cancer of well recognized premalignant state and readily accessible lesions for histological and molecular evaluation, our findings will also have a broad impact in the field, as they will enable the development of metformin as an effective, safe, and low-cost preventive agent for multiple malignancies.